plate_thumbs_11160

To address the poor thumbnail performance in large plates (ticket #11160) we use size 96 thumbnails so that we get the cached thumbnails (instead of generating them each time).

We still want to display them at the same size as before, so we need to add width and height attributes to each thumbnail. 

To test, load a plate of thumbnails, right click on a thumbnail in the browser and choose to "View Image". Check that the url of the image ends with "96" ie: webgateway/render_thumbnail/<imageId>/96/.
There should also be a noticeable speed increase on loading thumbs in plates.